The present invention is concerned with apparatus and methods for mining subterranean material, and more particularly with a coal mining machine and method for removing coal from beneath the surface of the earth with minimal disturbance of the overburden.
The demands of industry and society today require the utilization of all known energy sources. In many parts of the United States and other areas of the world, there exists an abundance of coal lying at a shallow depth below the surface of the earth. These coal deposits represent a potential source of relatively easily accessible and inexpensive fuel. The primary means of recovering this shallow lying coal is by strip mining, that is removing the overburden including top soil and foliage and then digging directly into the coal deposits. After the strip mining has been completed, the land is sometimes left without any treatment or attempt at restoration. In the absence of trees, grass and other types of foliage, soil erosion runs rampant due to flooding and wind storms. Moreover, the inversion of the overburden and the top soil exposes pyrites and other metallic ores to rapid oxidataion thereby weakening and leeching the soil and polluting adjoining waterways for many years. Thousands of acres of desolate land, particularly in the eastern United States, may be seen today as evidence of the destruction rendered by strip mining techniques.
The interest today of many private and governmental conservation entities in preserving the environment has led to various pressures on the coal mining industry to restore, at least in some measure, the landscape of strip mined areas and to seek alternate, less destructive methods for recovering shallow-lying coal. Despite considerable efforts by some coal mining companies to restore the land and leave it somewhat productive, it is doubtful that complete restoration can ever be accomplished on land which has been strip mined by present methods.
Moreover, alternate methods of mining shallow coal have been too expensive to be practical in many cases. One alternate approach is to utilize the methods of "longwall mining", a technique now limited to very deep coal beds where bedrock makes support relatively easy. Instead of removing the overburden, miners dig a narrow trench alongside the coal seam and a long tunnel horizontally along one end of the seam to form a passageway for setting up longwall machinery, including cutters, hydraulic roof supports and conveyors. As the cutters and conveyors work along the wall of the coal seam, new supports are erected next to the cutters and the old supports are removed allowing the roof to cave in and the overburden to drop. Thus, a considerable length of coal seam is mined but only a narrow trench need be refilled after the operation has been completed.
This technique is still in the experimental stage and it is yet to be seen whether longwall mining can be utilized in recovering shallow coal deposits. However, even if this approach is feasible, there are several disadvantages. Because of the need to constantly remove hydraulic roof supports and erect new roof supports, it is necessary that a number of miners work in the underground tunnel in close proximity to the cutters and conveyors. These workers are subject to the substantial danger of cave-ins because of the continual erection of new supports and the removal of old supports. The miners working near the equipment also face the possibility of becoming caught in the drilling and conveying systems. Furthermore, longwall mining would require substantial and expensive air conditioning equipment in order to make the underground excavation livable for miners. In addition, frequent shutdowns of the drilling and conveying apparatus could be expected in order to erect new hydraulic roof supports as the equipment moves forward against the wall of the coal seam. Finally, maintenance and servicing of the cutting and conveying systems and the hydraulic roof supporting system would be substantial.
The present invention concerns coal mining apparatus and methods for mining shallow coal deposits with minimal disturbance of the overburden. A remotely controlled underground mining machine having rotary cutters is directed along an underground coal seam. The coal is excavated from the underground machine through a vertical elevator to the surface to be loaded onto transport vehicles. A surface machine is connected to the vertical elevator and moves with the underground machine to provide guidance for the elevator shaft. A digging chain rotates around the vertical elevator shaft to cut a passageway for the shaft to move through the overburden as the underground machine and the surface machine advance. Fill dirt, cut by the digging chain, is dumped behind the surface machine to refill the passegeway. The overburden is gradually lowered by a slanted protective shield above the underground machine to fill the excavated area behind the underground machine.
In one aspect of the present invention, apparatus for removing subterranean material includes underground mobile means for moving beneath the overburden into the subterranean material. Mining means are connected to the mobile means for removing the subterranean material, and support means are mounted on the mobile means to move with the mobile means beneath the overburden and support a portion of the overburden above the mobile means.
In accordance with another aspect of the present invention, mining apparatus for removing coal from a subterranean coal seam utilizes a mobile mining machine with cutting means on the front for breaking the coal seam into separate pieces. A conveyor removes the coal pieces from in front of the mining machine, and a driving means moves the mobile mining machine forward as the cutting means and the conveyor open a passageway in the coal seam. A support means holds the overburden above the mobile mining machine and said cutting means to facilitate removal of the coal pieces. In accordance with a further aspect of the present invention, an elevator means is attached to the mobile mining machine and extends vertically upward to the surface. The elevator means includes a lifting elevator for transporting the coal pieces to the surface and digging means to cut a passageway for the elevator to move through the overburden. A surface vehicle is attached to the elevator means and is coordinated to move together with the underground vehicle and the elevator means.
In accordance with yet another aspect of the present invention, apparatus for moving subterranean material to the surface of the earth, includes mobile underground means, transporting means and mobile surface means. The underground means is moveable in the direction of the subterranean material and is adapted to process the material for conveying to the surface. The transporting means is connected to move in coordination with the mobile underground means and the mobile surface means and transports the processed material to the surface. The mobile surface means attached to the transporting means moves in coordination with the mobile underground means to receive processed subterranean material from the transporting means.
In another aspect of the present invention, a vertical shaft means extends from a mobile underground digging means to the surface of the earth for removing subterranean material from beneath the earth. Means are provided on the vertical shaft means for transporting the subterranean material to the surface. Drive means are mounted on the shaft means for moving the shaft through the earth in coordination with movements of the underground digging means.
Another aspect of the present invention includes mobile underground means for burrowing into subterranean material. Digging means break up the subterranean material and drive means moves the mobile underground means into the material. Transporting means are moveable with the mobile underground means to convey the subterranean material to a loading station.
In accordance with still another aspect of the present invention, a process for removing subterranean material uses a mobile underground mining machine. The overburden is supported above the mining machine and the subterranean material is processed into transportable form. The processed material is conveyed through the overburden to the earth surface and the supported overburden is lowered behind the mobile mining machine as the machine moves forward through the subterranean material.
Another aspect of the present invention concerns a process for removing subterranean material using a mobile underground mining machine continually moving toward the subterranean material. The material is broken into transportable pieces by the mining machine and lifted by a conveyor through the subterranean material to the surface. A passageway is continually cut through the overburden for the conveyor, which extends from the mining machine to the surface, so that the conveyor can move through the overburden in coordination with the mining machine. Another aspect of the present invention includes a process for mining coal from an underground coal deposit using a mobile underground machine, a mobile surface vehicle and an interconnecting conveyor shaft. The underground machine burrows into the coal deposit and breaks the coal into transportable pieces. The pieces are conveyed through the overburden by the conveyor shaft to the mobile surface vehicle. The surface vehicle is driven in coordination with the underground machine and a passageway is cut through the overburden to provide a path for the conveyor shaft to move in coordination with the underground machine and the surface vehicle.
It can be seen from the foregoing that the present invention provides many advantages over previous mining apparatus. A shallow underground coal deposit may be removed with a minimum of disturbance of the surface above the coal. The narrow trenches that must be dug are subsequently filled by the dirt taken from the trenches. The overburden is lowered gradually behind the underground digging machine so as to cause little, if any, disturbance. The mobile trenching shaft cut between the underground machine and the surface vehicle to facilitate the separation of the overburden above the mined portion of the deposit from other subterranean material to allow the overburden to settle evenly behind the machine. The underground machine is controlled and powered remotely by a surface vehicle so so that underground workers are not needed. Extensive use of hydraulic supports and longwall cutting equipment is not required. The conveyor system of the present invention provides a simple means for transporting coal to the surface and loading it onto transport vehicles. Ready access to the underground machine is allowed through the trenching shaft.